The present invention relates to a patterning method, a method of manufacturing an organic field effect transistor, and a method of manufacturing a flexible printed circuit board.
Field effect transistors (FET) including thin film transistors (Thin Film Transistor; TFT) used in many electronic apparatuses at present each includes, for example, a channel formation region and source/drain regions formed on a silicon semiconductor substrate or a silicon semiconductor layer, a gate insulation layer of SiO2 formed on a surface of the silicon semiconductor substrate or a surface of the silicon semiconductor layer, and a gate electrode provided opposite to the channel formation region through the gate insulation layer. Alternatively, the field effect transistor includes a gate electrode formed on a support, a gate insulation layer formed on the support inclusive of the area on the gate electrode, and a channel formation region and source/drain electrodes which are formed on the gate insulation layer. In the manufacture of the field effect transistors having these structures, very expensive manufacturing apparatuses for manufacturing the semiconductor devices have been used, and there is a keen request for lowering the manufacturing cost.
In view of the above, in recent years, attention has been paid on the research and development of an FET which uses an organic semiconductor material and which can be manufactured based on a method not using a vacuum technology, represented by a printing method, and the performance of the FET has come to be within an inch of the practical use level.
Conventionally, a patterning method in which a pattern composed of a hydrophilic region and a hydrophobic region is formed on a surface of a substrate and patterning is conducted by using this as a printing plate has been well known as offset printing method. Inks used in the offset printing method are usually high in viscosity, but an example of patterning in which low-viscosity liquid materials are used has also been reported.
Besides, Michael L. Chabinyc, et al., “Organic polymeric thin-film transistors fabricated by selective dewetting”, APPL. PHYS. Lett 81.4260-4262(2002) (hereinafter sometimes referred to as Reference 1) discloses a technology in which a wax is applied to a substrate by printing, an SAM (Self-Assembled Monolayer) is built up on a substrate region not covered with the wax, then the wax is removed, and an organic semiconductor material is built up on the region having been covered with the wax (in this region, the SAM is not formed). The organic semiconductor material is built up by immersing the substrate in a solution of the organic semiconductor material and then pulling up the substrate vertically.
Alternatively, technologies in which a coating liquid containing an organic semiconductor material is applied to a substrate by a die coating method, a dip coating method, or a spin coating method have also been known.